1. Field of the Invention
This invention relates to processes and compositions for purifying edible cooking oils. The compositions and processes of the present invention remove various oil contaminants such as color bodies, polar materials, soaps, fatty acids and trace metals, thereby improving the quality of, and extending the usable life of, the oil.
2. Description of Related Art
Edible frying oils, which are typically used to fry various foods such as chicken, French fries, potato chips, and other meat, vegetable or dough products, can decompose over time and with use due to the formation and acquisition of various contaminants released or produced during cooking. Contaminants such as water, soaps, polar compounds, polymers, free fatty acids, color bodies, and trace metals build up in the oil over time and contribute to the degradation and increased instability of the oil. As these contaminants build up in the oil, the oil can become discolored, develop a displeasing smell and taste, begin to foam due to the formation of soaps, produce heavy smoke at normal cooking temperatures, and/or quickly become rancid and unusable.
Without treatment this degeneration typically occurs rapidly, requiring complete replacement of the used oil with fresh oil as often as every 2 or 3 days, thereby significantly raising the cost of production of fried foods. The FDA Food Safety and Inspection Service (FSIS) Meat and Poultry Inspection Manual provides guidelines that must be observed by industrial meat and poultry fryers. For instance, Section 18.40(a), directed to frying of meat, explains that the suitability of fats and oils used for deep fat frying xe2x80x9ccan be determined from the degree of foaming during use or from color, odor, and flavor.xe2x80x9d Additionally the Manual indicates that xe2x80x9cfat or oil should be discarded when it foams over the vessel""s side during cooking, or when its color becomes almost black as viewed through a colorless glass container.xe2x80x9d Of course, the amount of time that fats and oils may be used for frying varies depending upon a number of factors, such as the type and volume of food fried, the temperature, the quality of new oil or fat added and the frequency of addition or new oil or fat, as well as the treatment used for decontamination of the oil.
The various contaminants that accumulate in the oil create several problems with the oil and the food fried in the oil. For instance, the high cooking temperatures and the water released from the food being fried causes the formation of free fatty acids. The free fatty acids combine with various trace metals in the oil to form soaps. Soaps not only cause unpleasant foaming of the oil, which can present a safety hazard for those operating the frying equipment, but also cause the food to absorb more of the oil during cooking. The absorption of more oil not only results in a greasier, less desirable product but may also result in the food product becoming overcooked, giving it a harder or tougher consistency than desired.
The accumulation of polar compounds is another serious problem in used oil. Polar compounds contribute to unpleasant taste and increased oxidation which leads to the oil becoming rancid and completely unusable. A build up of polar compounds in the oil also leads to a reduction in the smoke point of the oil. Carmelization, caused by buildup of color bodies that turn the oil a darker color, produces fried food with a darker, overcooked and unappealing appearance. Trace metals such as magnesium, phosphorous, copper, and iron also increase the oxidation of the oil by reacting with oxygen in the air to catalyze the oxidation process. This increases the peroxide value of the oil indicating increased instability and promoting further oxidation and rapid spoiling of the oil.
Combinations of impurities, such as free fatty acids and polar compounds can result in the formation of a film on the surfaces of the frying equipment. Additionally, buildup of fat and other impurities will reduce the smoke point of the oil, causing the oil to smoke heavily at operating temperatures of around 300xc2x0 F. To prevent the problems associated with the buildup of these contaminants, oil must either be replaced often, or treated to remove or neutralize the contaminants, thereby extending the life of the oil.
Known cooking oil treatments, or xe2x80x9cfrying aids,xe2x80x9d have various drawbacks. For instance, some treatments do not address more than one or two of the above-mentioned problems, while others fail to significantly extend the life of the oil, and some even introduce additional health and/or safety concerns. One method directed to reducing soap formation involves heating the oil to 300xc2x0 F. and mixing the oil with a composition of water, a porous carrier and a food-compatible acid. Similarly, another method involves contacting the oil with a food-compatible acid to help counteract soap formation. Both of these methods help eliminate soaps, but fail to address the other problems caused by contaminants present in the oil.
Another method for treating oil attempts to reduce the accumulation of free fatty acids and raise the smoke point of used cooking oil by mixing the used oil with an adsorbent of alkaline earth oxides or carbonates, which adsorbent is then separated out of the oil after mixing for between 3 and 15 minutes. In another method, used cooking oil is contacted with a composition of activated clay or magnesium silicate and between 15% to 75% weight of gel derived alumina to reduce both the amount of free fatty acids present in the oil as well as remove color from the oil. Yet another method for reducing the fatty acid content of used oil discloses contacting the oil with hydrated magnesium silicate. Once again, these methods treat only one or two problems with the used oil, thereby failing to significantly extend the overall shelf life of the oil.
One method for treating oil uses various silicas and acid-treated silicas to remove trace metals and phospholipids from used cooking oils, but fails to remove any other contaminants from the oil. In another treatment the used oil is contacted with a composition of 60% to 80% amorphous silica and 20% to 40% alumina. However, this method is ineffective in extending the life of the oil beyond about 5-10 days because the treatment fails to adequately reduce the levels of various contaminants. Moreover, each treatment with this product absorbs approximately 6 oz of oil for each 6 oz of the composition, thereby requiring frequent addition of more fresh oil.
Another method utilizes a metal-substituted silica xerogel having pH of at least 7.5 and optionally combined with an organic acid. This method is directed to removing contaminants such as phospholipids, soaps, metals and chlorophyll from glyceride oils. However the silica xerogel composition does not effectively decolorize the oil, and smoking of the oil occurs within about 5 days of use. As a result, oil treated with the silica xerogel will still require replacement after only about 5 to 7 days of use and treatment with the silica xerogel.
A commonly used treatment for frying oils is Silasorb(trademark) (Celite corporation, Denver, Colo.), a synthetic calcium silicate. This treatment lowers free fatty acids in the oil by a combination of adsorption and neutralization. However, the neutralization of a fatty acid with an alkaline metal produces a fatty acid soap and may result in uncontrollable foaming, leading to safety hazards for operators of frying equipment. Additionally, Silasorb contributes to the darkening of the oil.
Yet another method directed to removal of free fatty acids from used oil involves treating a used cooking oil or fat with a composition of magnesium silicate and at least one alkali material. Whereas many other treatments involve contacting the oil with a composition that absorbs the contaminants in the oil, the composition of this method works at least in part by neutralization. For instance, the magnesium silicate acts as a bleaching agent to change the color of the color bodies within the oil, thereby lightening the color of the oil. However, the disadvantage to this method is that the magnesium silicate creates polar compounds as a byproduct of the neutralization process. The presence of additional polar compounds reduces the smoke point of the oil and increases the oxidation of the oil, which accelerates spoiling and may give the oil an unpleasant taste and/or odor. The magnesium silicate also increases the levels of certain chemicals, including unsaturated aldehydes such as 2,4-decadienal and 2,4-hexadienal, responsible for changes in flavor of fried food products. Repeated use of the compound imparts a metallic taste to chicken fried in the treated oil. These changes render food cooked in the treated oil unappealing to the average consumer. Additionally, the magnesium silicate generates excessive amounts of soap, and the oil begins to smoke after only 10 days of use and requires replacement in less than 2 weeks.
None of these existing methods and compositions have adequately addressed the removal of the several contaminants that contribute to the degradation of the oil, but have instead individually attacked the particular contaminant perceived to be the greatest concern in a particular system. Additionally, these treatments fail to significantly extend the life of the oil by eliminating enough of each contaminant to enable continued re-use of the oil beyond more than a few days.
Thus, what is needed in the art are compositions and methods for quickly and effectively reducing the amount of several contaminants such as polar material, color bodies, soaps, free fatty acids and trace metals, such that regular treatment with the compositions and methods significantly extends the useable life of the oil, thereby reducing health risks and costs of fried food operations.
The invention relates to methods and compositions for reducing the accumulation of contaminants in edible oils used for cooking food products and enables continued recycling of the oil while preserving the taste and quality of the oil and food cooked in the oil. As used herein, the term xe2x80x9ccontaminantsxe2x80x9d refers to any component that, upon accumulation in the oil, adversely effects the useful life, taste, or other properties of the oil. Such contaminants include but are not limited to water, soaps, polar compounds, free fatty acids, color bodies and trace metals.
In its broad aspects, the invention relates to a process for treating an edible cooking oil with a composition of silica, acidic alumina, clay, and citric acid. More particularly, the oil is contacted with the composition, heated, and then separated from the composition.
The invention provides methods and compositions for significantly reducing the accumulation of undesirable contaminants in cooking oil. Treating the oil with the composition of the invention removes contaminants from the oil, improves the color, flavor, smell and shelf life of the oil, and reduces the incidence of smoking and foaming of the oil. The invention further provides methods and compositions which are cost effective and extend the usable life of the oil, thereby further reducing the cost of producing fried foods.
In its broad aspects, the composition of the invention contains a mixture of silica, acidic alumina, clay and optionally, citric acid. The composition contains these ingredients in amounts effective to remove contaminants such as free fatty acids, polar materials, color bodies, metals and soaps. The removal of these contaminants reduces the incidence of foaming and smoking, preserves the color and flavor of the oil and extends the usable life of the oil.
The methods and compositions of the invention work quickly and efficiently and have been demonstrated to reduce the buildup of polar material, trace metals, free fatty acids and other contaminants as well as to prevent and counteract soap formation and smoking. The methods and compositions provided successfully remove contaminants at temperatures between 160xc2x0 to 400xc2x0 F. without migration, i.e., without creating a powder deposit on the surface of the oil or equipment, which has been known to occur with the use of existing oil treatment products.
Use of the methods and compositions of the invention in frying equipment in the fast food business has been demonstrated to reduce fat buildup in the frying equipment by approximately 98% and to extend the usable life of the oil up to 45 days without replacement. The invention also absorbs less oil during treatment, requiring less frequent addition of fresh oil. For instance, as described above, some existing oil treatments absorb up to as much as 6 oz of oil for every 6 oz of treatment material, per treatment; however, the composition of the present invention absorbs only about 2 oz of oil for every 6 oz of composition, thereby requiring less frequent addition of new oil.
The invention not only provides health benefits by decreasing contaminants, indigestible polymers and oxidized components, but also improves the taste of fried food cooked in the treated oil. The methods and compositions of the invention will also decrease significant health risks associated with used oil as well as reduce the production costs of fried foods.
These and further advantages of the present invention will become apparent after a review of the following detailed description of the disclosed embodiments.